CNS Infections - Cochran Flashcards
Describe the four routes of access that infectious agents may take to reach the brain.
Hematogenous - Either arterial or retrograde venous.
Local extension - eg Infected tooth
Neural route - eg Retrograde neuronal
Direct implantation - eg Surgical infection
Many CNS infections are caused by pathogens that are specific to nervous tissue (“neurotropic”); describe some mechanisms by which this may occur.
Viral-specific receptors on nervous tissue
Capsular proteins (unclear how this facilitates neurotropism)
Viral spread along nerves (eg Herpes)
What are the classic symptoms in meningitis?
Describe the most likely pathogens in meningites with a <24hr, 2-7day, or longer history.
Headache, nuchal rigidity, fever, photophobia, and clouded consciousness.
Hyperacute (<24hr) = Meningococcus
Acute (2-7days) = Other bacteria (Strep pneumo, HiB)
Subacute/chronic (>1 week) = Tuberculosis, syphilis
Bacterial meningitis is highly dangerous and often fatal. Describe its gross and microscopic morphology.
What will a CSF yield?
Purulent exudate under the meninges, with vasculitis and congestion. Abundant neutrophils in subarachnoid space.
High neutrophils and low glucose. Bacteria should be present for gram staining, PCR or culturing.
Brain abscesses can be seen in bacterial or viral CNS infections. Describe the abscess and the usual culprits.
Focus of infection circumscribed by fibroblasts/collagen and gliosis. (“Ring-enhanced”)
Strep and Staph species are most common. Weird bugs seen in the immunocompromised… (toxo, nocardia, listeria, fungi, TB)
Infection of the brain parenchyma is known as _____. It may be caused by bacteria, viruses, or fungi. The three major bacterial causes are ___________.
Encephalitis; bacterial eg Tuberculosis, Syphilis, and Borrelia (lyme disease).
Who is most often afflicted by TB encephalitis?
Describe its gross and histologic morphology.
The immunocompromised mostly, but ~15% of anyone with acute TB.
Mostly involves the brain base. Granulomas (“Tuberculomas”) feature classic pattern with epithelioid histiocytes and giant cells surrounding caseating core.
What is tuberculosis of the spine known as?
What are its complications?
Pott’s disease (TB spondylitis)
Epidural abscesses in the spinal cord cause cord compression, vertebral collapse.
Tertiary syphilis has three major forms.
Describe paretic neurosyphilis. Include gross and micro morphologies!
In paretic neurosyphilis, the meninges thickens causing brain atrophy and subsequent cognitive and motor impairment. CSF outflow is impaired.
Histology reveals lymphocytosis with plasma cells and microglia.
Tertiary syphilis has three major forms.
Describe Meningovascular syphilis. Include gross and micro morphologies!
Heavy involvement at the base of the brain causes arteritis–collagenous thickening of wall & vascular compromise cause infarcts, hydrocephalus. Focal deficits seen.
Looks like a fibrinoid necrosis…
Tertiary syphilis has three major forms.
Describe Tabes Dorsalis. Include morphology and presentation!
Involvement of the posterior cord (cuneate and gracile) cause loss of discriminative touch and proprioception (leads to broad shuffling gait). Lightning pains & paresthesias also experienced.
Myelin stains reveal demyelination in the posterior columns.
Viral CNS infections are generally (more/less) severe than bacterial.
Describe the three characteristic microscopic findings of viral encephalitis.
Less severe! (Rule of thumb; always exceptions eg Rabies)
- Perivascular lymphocytic infiltrate.
- Microglial nodules (rod-shaped)
- Neuronophagia (inflammatory cells surround neuronal remnant)
HSV-1 is one of the most common viral encephalites.
It has a distinctive clinical presentation, describe it.
What will imaging reveal?
Affects mood, memory, and behavior. Makes you act “crazy”!
MRI will reveal foci of involvement mostly in the frontal or temporal lobes.
What are the complications of herpes simplex encephalitis?
How can it be diagnosed?
Congestion, swelling, hemorrhagic necrosis.
PCR for viral DNA, or check histology for Cowdry Type A bodies.
HSV-2 and VZV are less likely to cause encephalitis than HSV-1. Describe who generally would get encephalitis from them.
HSV-2: Neonates infected through birthing.
VZV: Older patients experiencing reactivation (scarring, painful; lymphocytes present in nerve ganglia)
This is a histologic finding that is characteristic of a particular viral infection. Name the infection, and name what’s pictured.
Hint: These are eosinophilic, not basophilic.
Cowdry Type A bodies - Herpes encephalitis
(Thought of owl’s-eye inclusions? Those are basophilic)
A 40yo male patient presented with a CD4+ count of ~50. He developed convulsions, hallucinations, and finally died of a hemorrhagic infarct.
Pictured is his brain post-mortem. What is the diagnosis?
Cryptococcus neoformans; the classic soap-bubble lesions are presented and the patient clearly has AIDS.
A 30yo female patient presents with complaint of headache, fever, and drowsiness. You aren’t eager to biopsy her brain yet, but if you did, you would find this.
What is pictured, and what other findings would you also expect based on the differential?
This is neuronophagia, a histologic sign of viral encephalitis. The other two signs are lymphocytosis (perivascular and/or parenchymal), and microglial nodules.
